A diaphragm valve using a diaphragm as a valve body has been conventionally well known. The conventional diaphragm valve is shown in FIG. 3 and FIG. 4.
In FIG. 3, a diaphragm valve 1 includes a block-like body 2 having a fluid inflow channel 2a, a fluid outflow channel 2b, and a depression 2c opening upward, a cylindrical hood 3 having a lower end portion screwed into an upper portion of the depression 2c of the body 2 and extending upward, a casing 4 screwed into the hood 3, an annular seat 5 made of synthetic resin and disposed on a circumferential edge of the fluid inflow channel 2a, a diaphragm 6 that is pressed against or separated from the seat 5 to open and close the fluid inflow channel 2a, a diaphragm presser 7 that presses a central portion of the diaphragm 6, and an actuator (not shown) that is built in the hood 3 and the casing 4 and causes the diaphragm 6 to press against and separate from the seat 5 via the diaphragm presser 7.
As shown in FIG. 4 in an enlarged scale, on a bottom surface 2d of the depression 2c of the body 2, an annular inner projection 12 having a relatively small diameter and an annular outer projection 13 having a relatively large diameter are provided, and the seat 5 made of synthetic resin are inserted between the inner projection 12 and the outer projection 13. The inner projection 12 is caulked radially outward and the outer projection 13 is caulked radially inward, whereby the seat 5 made of synthetic resin is prevented from coming off.
Patent Literature 1 discloses that the inner projection is caulked whereby the seat is prevented from coming off.